Yamaha EM5014C - Manual (Page 14)

14 EMX5014C Owner’s Manual
Making the Most of Your Mixer
Mixer Basics
A balanced cable has three conductors:
1) A ground conductor which carries no signal, just the “ground” or “0”
reference against which the signal in the other conductors fluctuates.
2) A “hot” or “+” conductor which carries the normal-phase audio signal.
3) A “cold” or “–” conductor which carries the reverse-phase audio signal.
Signal Levels and the Decibel
Let’s take a look at one of the most commonly used units in audio: the decibel (dB). If the smallest sound that
can be heard by the human ear is given an arbitrary value of 1, then the loudest sound that can be heard is
approximately 1,000,000 (one million) times louder. That’s too many digits to deal with for practical calculations,
and so the more appropriate “decibel” (dB) unit was created for sound-related measurements. In this system
the difference between the softest and loudest sounds that can be heard is 120 dB. This is a non-linear scale,
and a difference of 3 dB actually results in a doubling or halving of the loudness.
You might encounter a number of different varieties of the dB: dBu, dBV, dBM and others, but the dBu is the
basic decibel unit. In the case of dBu, “0 dBu” is specified as a signal level of 0.775 volts. For example, if a
microphone’s output level is –40 dBu (0.00775 V), then to raise that level to 0 dBu (0.775 V) in the mixer’s
preamp stage requires that the signal be amplified by 100 times.
A mixer may be required to handle signals at a wide range of levels, and it is necessary match input and output
levels as closely as possible. In most cases the “nominal” level for a mixer’s input and outputs is marked on the
panel or listed in the owner’s manual.
Hot
Cold
Shield
(Ground)
Outer
Insulation
Balanced Unbalanced
+ 20 dBu
0 dBu 0.775 V
-20 dBu
-40 dBu
-60 dBu
The inputs and outputs on home-use audio gear
usually have a nominal level of –10 dBu.
Most professional mixers, power amplifiers, and other
types of equipment have inputs and outputs with a
nominal level of +4 dBu.
Microphone signal levels vary over a wide range
depending on the type of microphone and the source.
Average speech is about –30 dBu, but the twittering of
a bird might be lower than –50 dBu while a solid bass
drum beat might produce a level as high as 0 dBu.